Light-weight live-floor module for trailers

ABSTRACT

The light-weight live-floor module has a floor surface, parallel cables laid on the floor surface, a length of conveyor belt laid on the cables, a movable bulkhead and a winch system for moving the belt, the cables and the bulkhead back and forth in unison, such as a shuttle. The belt has just enough length to cover the return axis and the floor surface on which goods are transported, thereby reducing any unnecessary weight in the live floor structure. The cables and the belt are wrapped over different axes for eliminating relative movement between the cables and the belt. One axis is set higher than the floor surface for easily breaking static friction under the belt. In a method for breaking static friction between a conveyor belt and a floor surface, a first segment of the belt is jolted upwardly while tension is applied in the belt.

This application is a continuation application of application Ser. No.12/805,155, filed Jul. 15, 2010 which claims the benefit of U.S.Provisional Application No. 61/282,065 filed Dec. 10, 2009.

FIELD OF THE INVENTION

The present invention pertains to the field of live-bottom trailers, andmore particularly it pertains to live-bottom trailers using a conveyorbelt that is movable along the floor of the trailer, and cables mountedunder the conveyor belt to reduce friction between the conveyor belt andthe floor of the trailer.

BACKGROUND OF THE INVENTION

The live-bottom trailers that are of interest herein are used in roadconstruction to haul sand, gravel, rocks, broken pavement and newasphalt. Live-bottom trailers having conveyor belts movable along thefloors thereof also include agricultural trailers used for haulingpotatoes and other vegetable or grains from a harvester. Knownlive-floor trailers also include highway transport trailers that areused for transporting dry freight in boxes and on pallets.

Common live-bottom trailers have a conveyor-type rubber belt slidingover the floor of the trailer for moving the content of the trailertoward the rear door of the trailer and for speeding up the unloading ofthe trailer. The same conveyor belt is also used for more easily loadingthe trailer. These highway trailers and semi-trailers can carry severaltons of material.

Examples of these live-bottom trailers found in the prior art aredescribed in the following documents:

-   U.S. Pat. No. 3,498,482 issued to M. Lewis on Mar. 03, 1970;-   U.S. Pat. No. 3,593,864 issued to W. H. Moser on Jul. 20, 1971;-   U.S. Pat. No. 3,704,798 issued to H. L. Carpenture, Jr. et al. on    Dec. 05, 1972;-   U.S. Pat. No. 3,722,717 issued to L. K. Stryczek on Mar. 27, 1973;-   U.S. Pat. No. 3,888,366 issued to E. D. Prahst on Jun. 10, 1975;-   U.S. Pat. No. 3,953,170 issued to J. O. Webb on Apr. 27, 1976;-   U.S. Pat. No. 3,998,343 issued to V. E. Fors on Dec. 21, 1976;-   U.S. Pat. No. 4,162,735 issued to M. Lewis on Jul. 31, 1979;-   U.S. Pat. No. 4,431,360 issued to M. Maeno in Feb. 14, 1984;-   U.S. Pat. No. 4,518,303 issued to W. H. Moser on May 21, 1985;-   U.S. Pat. No. 4,664,583 issued to J. N. Gust on May 12, 1987;-   U.S. Pat. No. 4,747,747 issued to S. M. Fusco et al. on May 31,    1988;-   U.S. Pat. No. 4,842,471 issued to G. L. Hodgetts on Jun. 27, 1989;-   U.S. Pat. No. 6,837,668 issued to D. J. B. Brown on Jan. 4, 2005;-   U.S. Pat. No. 7,147,423 issued to R. Golden et al. on Dec. 12, 2006.

In another type of live-bottom trailers, the load inside the trailer ismoved on steel cables that are laid along the floor of the trailer. Inthese applications, a conveyor belt is not used. The cables are pulledalong the floor of the trailers by winches or hydraulic cylinders, forcarrying the load over the floor surface. Because the total surface ofthe cables that is in contact with the floor of the trailer is smallerthan the footprint of the load to be moved, and because there is alesser coefficient of friction provided by the cables, the forcerequired to overcome friction is considerably reduced.

Examples of trailers in the prior art, having parallel cables laid onthe floor thereof are listed below:

-   U.S. Pat. No. 3,272,358 issued to F. Thompson on Sep. 13, 1966;-   U.S. Pat. No. 4,082,196 issued to D. W. Lutz et al. on Apr. 04,    1978;-   U.S. Pat. No. 4,111,318 issued to D. E. Lutz on Sep. 5, 1978;-   U.S. Pat. No. 4,113,122 issued to D. E. Lutz on Sep. 12, 1978;-   WO 87/01996 filed by Luigi Pellegrino, published on Apr. 9, 1987;-   U.S. Pat. No. 5,171,122 issued to L. Pellegrino on Dec. 15, 1992.

A number of prior art documents also disclose movable bulkheadarrangements for pushing the content of a trailer all at once toward therear door of the trailer. These documents are listed herein below forillustrating progress made in the art:

-   U.S. Pat. No. 2,606,677 issued to A. E. Snedeger on Aug. 12, 1952;-   CA Patent 1,031,735 issued to H. D. Rezac on May 23, 1978;-   U.S. Pat. No. 5,143,508 issued to D. E. Lutz et al. on Sep. 1, 1992;-   U.S. Pat. No. 5,314,290 issued to D. E. Lutz et al. on May 24, 1994.

The various concepts described in the prior art have a common advantageof emptying a trailer in a more efficient manner. Although theadvantages of a conveyor belt; a series of parallel cables moving on thebottom surface of a trailer, and a movable bulkhead are easy toappreciate, a combination of the three elements wherein the cables areused to move both the conveyor belt and the bulkhead, has not been seenin the prior art. This deficiency in the art may be explained by thechallenges that this combination represents to designers and builders ofthese trailers.

One of the challenges encountered in the design and construction of alive-bottom trailer with floor cables mounted under a conveyor belt is arelative movement between the conveyor belt and the floor cables. Thisrelative movement could causes the gouging of grooves in the bottomsurface of the belt and can destroy the belt in a relatively short time.

Another challenge is a total weight of the combination. Truck owners areoftentimes paid by the ton of material transported. The weight ofaccessories mounted inside a trailer takes away available space andavailable cargo weight for that trailer. Therefore the advantages of alive-floor mechanism must have sufficient value to offset the losses inrevenue from a reduction of cargo weight for that trailer.

It is believed that this weight restriction factor, primarily, has beena major impediment in the past for designing and building a live-bottomtrailer having a conveyor belt; parallel cables mounted under the beltand a bulkhead that is movable with the belt and cables.

SUMMARY OF THE INVENTION

100131 In the present invention, however, there is provided alight-weight live-floor module that has a floor surface, parallel cableslaid on the floor surface, a length of conveyor belt laid on the cables,a movable bulkhead and mounting arrangements that provide an outstandingweight-efficiency ratio. As a result, the tension required to move aload on the belt is provided in great proportion by the cables and in alesser extent by the belt.

In the following description of several aspects of the presentinvention, the scope of the invention should not be limited to a narrowinterpretation of the elements described and to the exact partsillustrated in the drawings. Therefore, generic terminology is usedherein where ever it is possible without reducing the clarity of thedescription. The expression “goods-carrying sheet” is used to designatea conveyor belt made of thick rubber with one or more plies; a conveyorbelt made of interlinked metal links or mesh, or a belt made of fabric,fibreglass, nylon, webbing, canvas or similar flexible material.Similarly the word “pullers” should be understood as encompassingcables, ropes, strings, flat straps, chains, or other pulling elementshaving sufficient tensile strength to perform as expected. Also, theexpression “return axis” is used to designate a roller, a pulley, awheel or a static bumper on which a belt or a cable changes direction.

The expression “light-weight” is used herein because the load carriedand pulled on the live-floor module is shared by both the conveyor belt,and to a greater extend, by the cable system. Because the tension in thebelt is greatly reduced, the conveyor belt can be much lighter than inother conventional live-bottom trailers. Also the expression “live-floormodule” is used herein because its applications are not limited totrailers. The present live-floor module can be used as a base on which ahighway transport trailer is built. Similarly, the live-floor module canbe used as a base for building straight-frame box trucks, gravel-typesemi-trailers, or it can be used as a stand-alone conveyor on docks ofwarehouses for example for handling material in and out of transporttrailers. The live-floor module described herein can also be scaled downfor installation in cube vans and pickup trucks.

In one aspect of the present invention, there is provided a live floorcomprising a sheet return axis mounted to an extremity thereof and agoods-carrying sheet having first and second ends. The goods-carryingsheet is wrapped over the sheet return axis, with the first endextending above a plane of the live floor and the second end extendingbelow the aforesaid plane. There is also provided a mechanism connectedto the first and second ends for moving the goods-carrying sheet aboutthe sheet return axis for loading and unloading goods on thegoods-carrying sheet.

The goods-carrying sheet has just enough length to cover the sheetreturn axis and the floor surface on which goods are transported,thereby reducing any unnecessary weight in the live floor structure. Asit will be understood, the total length of the goods-carrying sheet is asame dimension or substantially a same dimension as the length of thelive-floor module itself. Also the goods-carrying sheet in thelive-floor module according to the present invention is made of athinner and a lighter material than a same arrangement on a live-floorsystem of the prior art.

In another aspect of the present invention, there is provided alive-floor module comprising first and second spaced-apart return axesmounted side-by-side on an extremity thereof. A series of parallelpullers are laid on a surface of the live-floor module; and agoods-carrying sheet is laid on the parallel pullers. The pullers areaffixed at their ends to extremities of the goods-carrying sheet. Thepullers are wrapped over the first return axis and the goods-carryingsheet is wrapped over the second return axis. This arrangement isadvantageous for eliminating relative movement between thegoods-carrying sheet and the parallel pullers when the goods-carryingsheet and the parallel pullers move around the extremity of thelive-floor module.

In yet another aspect of the present invention, there is provided alive-floor module comprising a floor surface; a roller mounted on anextremity of the floor surface; a series of parallel pullers laid on thefloor surface, and a goods-carrying sheet laid on the parallel pullers.The pullers are affixed at their ends to extremities of thegoods-carrying sheet. The pullers and the goods-carrying sheet arewrapped over the roller and the roller is mounted higher than the floorsurface. When tension is applied to the pullers and to thegoods-carrying sheet, the goods-carrying sheet is forced upwardly nearthe roller to break static friction between the goods-carrying sheet andthe floor surface near the roller.

Yet in a further aspect of the present invention, there is provided amethod for breaking static friction between a goods-carrying sheet and afloor surface. This method comprises the steps of jolting a firstsegment of the goods-carrying sheet upwardly, and simultaneouslyapplying a tension in the goods-carrying sheet. Because thegoods-carrying sheet and the pullers have some elasticity, the joltingmovement mentioned above and the simultaneous tension in thegoods-carrying sheet, set a longitudinal vibration that is propagatedalong the goods-carrying sheet to break static friction along thegoods-carrying sheet and the floor surface.

The upward jolt breaks the static friction under the first segment ofthe goods-carrying sheet. The longitudinal tension between the firstsegment of the goods-carrying sheet and the floor surface is suddenlyreleased. This tension is applied to a next segment which also causesstatic friction to break under that second segment, and so on until theentire goods-carrying sheet is set in motion. This phenomenon worksequally well with goods-carrying sheets loaded with gravel or dryfreight. Because of this initial upward jolt in the first segment of thegoods-carrying sheet, the breaking of the static friction is effected ina peeling-like action with less force and less work than in thelive-floors of the prior art.

This brief summary has been provided so that the nature of the inventionmay be understood quickly. A more complete understanding of theinvention can be obtained by reference to the following detaileddescription of the preferred embodiment thereof in connection with theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of a light-weight live-floor module is illustrated in theattached drawings. In these drawings the same numerals are used toidentify the same elements. In the drawings;

FIG. 1 illustrates a partial side, top and rear-end perspective view ofthe live-floor module according to the preferred embodiment of thepresent invention;

FIG. 2 is a partial side, top and front-end perspective view of thebasic structure of the live-floor module according to the preferredembodiment of the present invention;

FIG. 3 is a top view of the winch system for pulling the cables and drawbar assemblies along the preferred live-floor module;

FIG. 4 is a partial longitudinal cross-section view of the basicstructure of the preferred live-floor module, as seen substantiallyalong line 4-4 in FIG. 2;

FIG. 5 is a partial transverse cross-section view of the live-floormodule, as seen substantially along line 5-5 in FIG. 1;

FIG. 6 is a cross-section view through the discharge end of thelive-floor module as seen along line-6-6 in FIG. 1;

FIG. 7 is a graph illustrating the forces affecting the movement of theconveyor belt in the preferred live-floor module;

FIGS. 8, 9, and 10, are illustrations of other types of pullers that canbe used under the conveyor belt in replacement of the floor cables inthe preferred live-floor module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will be described in detailsherein one specific embodiment of a light-weight live-floor module foruse in trailers and warehouses. It should be understood that the presentdisclosure is to be considered as one example of the principles of theinvention and is not intended to limit the invention to the embodimentillustrated and described.

Referring firstly to FIG. 1, the preferred light-weight live-floormodule 20 has a base 22, two side walls 24, 26, and a movable bulkhead28. A live-floor system, generally designated as label 30 isincorporated into the base 22. In use, a load (not shown) is placed onthe live-floor system 30 between the side walls 24, 26 and the bulkhead28. A winch system 32 is mounted at the front end of the base 22 and itis used for moving the bulkhead 28 and the live floor toward thedischarge end of the trailer and back.

In the illustration of FIG. 1, the bulkhead 28 is shown in anintermediate position along its trajectory. It should be understood thatthe bulkhead 28 can be retracted close to the winch system 32 such thatthe cargo space available between the side walls 24, 26 is a large aspossible. In use, the bulkhead 28 is movable to the discharge end of thelive-floor module 20 and back such as a shuttle.

It will be appreciated that the live-floor module 20 illustrated in thedrawings can be equipped with an undercarriage of a semi-trailer or atransport trailer for example for hauling gravel or packaged freight.The live floor module 20 can also be mounted on a stationary supportframe for use in a warehouse.

Referring now to FIGS. 1-6, additional structural details of thepreferred live-floor system 30 will be explained.

The preferred live-floor system 30 comprises a plurality of spaced-apartparallel floor cables 34 that are attached at their ends to an upperdraw bar 36 and to a lower draw bar 38 respectively. The attachment ofthe floor cables 34 to the draw bars 36, 38 is preferably done usingcrimped-on clevis and turnbuckle (not shown), but can also be done usingother clamps and tighteners known in the field of cable ferrules andhardware.

The floor cables 34 are drawn tight between the draw bars 36, 38 andover respective return sheaves 40 at the discharge end of the base 22.

A length of conveyor belt 50 is drawn tight over the floor cables 34.The length of conveyor belt 50 is attached at its ends to the upper drawbar 36 and to the lower draw bar 38, respectively. The conveyor belt 50is stretched over a return roller 52 at the discharge end of the base22. The length of conveyor belt 50 is also movable back and forth withthe bulkhead 28 such as a shuttle.

The floor cables 34 are supported directly over a hard floor surface 54,such as hardwood or most commonly, metal plates. The conveyor belt 50 issupported in a large portion by the floor cables 34. Preferably, thehard floor surface 54 has rails 56 encased therein under each floorcable 34. These rails 56 are made of a low friction material such asTeflon™. These rails 56 will be described again later when makingreference to FIGS. 8-10.

It will be appreciated that when a load of dry goods on pallets iscarried on the live-floor module 20, that load is supported entirely bythe floor cables 34. When a load of gravel or other similar aggregatematerial is supported on the conveyor belt 50, the conveyor belt flexesand therefore, the belt is supported partly by the floor cables 34 andpartly by the hard floor surface 54.

Referring now to FIGS. 2, 3 and 4, the winch system 32 of the live-floormodule 20 and other structural details will be explained.

Firstly, the bulkhead 28 is attached to the upper draw bar 36. The upperportion of the bulkhead 28 has two saddle members 60 that are movablymounted over upper longitudinal rails 62 on the side walls 24, 26,respectively. These saddle members 60 are fastened to a pair of guidecables 64, 66 by crimp-type connectors 68 for example. Each one of theguide cables 64, 66 extends around a respective one of the walls 24, 26,on sheaves 70 at each corner of the walls. The guide cables 64, 66 formclosed loops and are also fastened by crimp-type connectors 68 orotherwise to the lower draw bar 38 for movement with the lower draw bar38.

A displacement of the lower draw bar 38 entrains a similar movement ofthe saddle members 60 and the bulkhead 28 in the opposite direction.Because the bulkhead 28 is driven by the upper draw bar 36 at its lowerend and it is driven by the guide cables 64, 66 at its top end,excessive strength in its structure is not required. The bulkhead 28needs only to be made of relatively small structural members such thatits weight is relatively light as compared to conventional bulkheads intrailers of the prior art. Also, the bulkhead 28 needs not to be guidedin T-slots or otherwise in the base 22 of the live-floor system 30. Itsattachments to the upper draw bar 36 and to the upper rails 62 aresufficient to fulfill its purpose.

The base 22 of the live-floor system 20 is made of structural steel andhas a passage “P” extending horizontally along its length. The returnportion of the conveyor belt 50 and floor cables 34 extend along thispassage “P”, as can be seen in FIGS. 4 and 6.

The base 22 has upper cross members 80 extending across the upperportion thereof, and lower cross members 82 extending across the lowerportion thereof. The base 22 has a gap between the upper cross members80 and the lower cross members 82. This gap defines the passage “P”.Other framing members are included in the base 22 to strengthen the base22 against bending, twisting and skewing. These additional framingmembers have not been illustrated herein because they do not representthe focus of the present invention.

Because of the passage “P” and the mounting of the conveyor belt 50 andthe lower draw bar 38 along this passage “P”, the preferred live-floormodule 20 is compact in thickness. The preferred live-floor module 20 isthereby usable as a modular floor for trucks. It is usable as an add-onfloor that can be strapped onto a sub-floor and taken out when needed,or it can be used as a stand alone unit on a loading dock of a warehousefor example. It will also be appreciated that the preferred live-floormodule 20 can be used without the bulkhead 28, or without the side walls24, 26, or without both the bulkhead and side walls to handle dry goodson pallets for example.

The winch system 32 is illustrated in greater details in FIG. 3. Thewinch system 32 is also built for strength and light weight. The winchsystem 32 has two pulley systems mounted in tandem and each giving amechanical advantage.

A first pulley system comprises a first pulley 92 mounted to the upperdraw bar 36 and a second pulley 94 mounted to the lower draw bar 38. Afirst winch cable 96 has an end segment 98 tied to a shock absorber 100that is mounted to a cross member 102 on the base 22. A second segment104 which is continuous with the end segment 98 extends around the firstpulley 92, and to the winch drum 90. It is wrapped several turns 106around the winch drum 90. A third segment 108 continuous with the secondsegment 104 extends from the turns 106 on the winch drum 90 to thesecond pulley 94 mounted on the lower draw bar 38. A fourth segment 110continuous with the third segment 108 extends around the second pulley94 and through to the cross member 102 to a second shock absorber 112that is mounted to the cross member 102.

The second pulley system is a mirror image of the first one, andtherefore, it is illustrated using the same labels as in the firstpulley system but with a prime symbol on each label.

Because there are two pulley systems mounted in tandem and each isgiving a mechanical advantage, the components of the winch system 32 aresmaller and lighter in weight than other winch system where a singlecable arrangement would have been used.

Referring now to FIGS. 6 and 7, two important aspects of the preferredlive-floor module 20 will be explained. Firstly, the discharge end ofthe live-floor module 20 has a series of cable return pulleys 40 mountedalong a same axis, and a belt return roll 52 that is mounted on adifferent axis than the series of cable return pulleys 40. The series ofpulleys 40 and the roll 52 are also referred to herein in a broadersense as return axes.

The reason for this mounting using separate roll and pulley axes is toavoid damaging the underside of the belt by a relative movement andassociated friction between the floor cables 34 and the underside of theconveyor belt 50. It will be appreciated that such damage would occur ifa same axis would have been used.

Secondly, the upper segments of the cable-return pulleys 40 are setslightly higher than the floor surface 54 of the live-floor system 30.The cable-return pulleys 40 are set higher by a dimension “H” asillustrated in FIG. 6. A dimension “H” of about one half inch issufficient for the intended purpose.

When tension is applied all at once in the floor cables 34 by the winchsystem 32 and by the lower draw bar 38, these floor cables 34 straightenup in a snap and cause a first segment “S1” of the conveyor belt 50 tobe jolted upward. This sudden upward jolt has the effect of breakingstatic friction between the conveyor belt 50 and the floor surface 54along at least the length of belt segment “S1”. The segments “S1”; “S2”;“S3”; etc, as illustrated in the drawings are not drawn to scale, andare used simply to facilitate the description of a phenomenon thatoccurs in the live-floor module 20 in use.

It is important to indicate again that the conveyor belt 50 is under thesame tension as in the floor cables 34 because of common attachments ofthe floor cables 34 and the conveyor belt 50 to the upper and lower drawbars 36, 38. It is also important to understand that both the conveyorbelt 50 and the floor cables 34 have a substantial yield strength andelasticity. The presence of the cables 34 ensures that both the cables34 and the conveyor belt 50 are not stretched beyond their respectiveelastic limit or yield strength, when an unloading phase of thelive-floor module 20 is initiated.

In order to facilitate the following explanation, the horizontal tensionin the conveyor belt 50 and in the floor cables 34 is represented by thebar-code-like symbols 120 in FIG. 7. The upward jolt given to the firstsegment “S1” of the conveyor belt 50 by the floor cables 34 isrepresented by the curve 122 in FIG. 7.

When the conveyor belt 50 is loaded with gravel for example, the upwardjolt 122 given to the conveyor belt 50 by the floor cables 34 is quicklydampened as illustrated in FIG. 7. However, this upward jolt 122 andassociated tension 120 in the floor cables 34 and in the conveyor belt50 cause static friction under at least the first segment “S1” to bebroken. Because kinetic friction is less than static friction, a largeportion of the tension 120 in the conveyor belt 50 and in the floorcables 34 is then suddenly released from segment “S1” and applied to anext segment “S2”.

The upward jolt 122 applied against the first segment “S1” is generatedin a snap and the static friction under the first segment “S1” is alsobroken in a snap. The release of the static friction under the firstsegment “S1” generates a horizontal shock wave along the conveyor belt50 that progressively moves as a flash along the conveyor belt 50.

Although the upward jolt 122 is quickly dampened by a load of aggregatematerial, the resulting horizontal shock wave 120 is only reduced by adifference between static and kinetic friction. As a result, staticfriction under the conveyor belt 50 is broken in a peeling motionwithout using great force in the conveyor belt 50. The conveyor belt 50used in the preferred live-floor module 20 is thinner and lighter inweight than the conveyor belts in other live-floor modules not havingfloor cables thereunder.

Because the weight of a live-floor module is greatly affected by thethickness of the conveyor belt, a reduction in the belt thickness has alarge effect on the total weight of the entire live-floor module.Because of the relatively low stress requirement in the conveyor belt50, because of the lighter winch 32 and the light-framed bulkhead 28, itis estimated that a reduction in weight of 5,000-6,000 lbs., isachievable with the preferred live-floor module 20 as compared tolive-floors of the prior art.

Another aspect of the preferred light-weight live-floor module 20 isexplained in FIGS. 8, 9 and 10. Although the preferred live-floor module20 has floor cables 34 that can be interpreted as being circular braidedsteel cables, it can be appreciated that equivalents pullers can be usedto obtain similar advantages as the floor cables 34. Some of theseequivalent pullers are flat straps 126 made of metal or plasticmaterial, as shown in FIG. 9 or power-transmission chains 128 as shownin FIG. 10.

Other equivalents for other components are also possible and therefore,the components, dimensions mentioned herein and the accompanyingillustrations should not be considered as limitation in the presentinvention.

1. A truck box having sides with an effective height and a live floorcomprising a floor surface, an axis mounted to an extremity of saidfloor surface, a goods-carrying sheet laid on top of said floor surface;said goods-carrying sheet having first and second extremities; a firstdraw bar affixed to said first extremity and a second draw bar affixedto said second extremity; said goods-carrying sheet being wrapped oversaid axis, with said first draw bar extending there across above saidfloor surface and said second draw bar extending there across below saidfloor surface; said first and second draw bars being guided for movementback and forth relative to said axis in parallel alignments with saidfloor surface; a mechanism connected to said first and second draw barsfor moving said first and second draw bars in opposite directionsrelative to each other and for moving said goods-carrying sheet aboutsaid axis for loading and unloading goods thereon; a bulkhead having anelevation corresponding to said effective height, an upper edge and alower edge; said lower edge being mounted to said first extremity ofsaid good-carrying sheet and to said first draw bar for movement withsaid first draw bar and said good-carrying sheet along said floorsurface; said sides of said box having sheaves mounted on upper cornersthereof; a first pair of cables affixed to said lower edge of saidbulkhead; said first pair of cables being threaded over said axis andbeing affixed to said second draw bar for movement of said bulkhead withsaid goods-carrying sheet, and a second pair of cables affixed to saidupper edge of said bulkhead; said second pair of cables being threadedover said sheaves and over said axis and being affixed to said seconddraw bar for movement of said upper edge of said bulkhead in unison withsaid lower edge.
 2. The truck box as claimed in claim 1 furthercomprising a series of parallel pullers extending between said floorsurface and said goods-carrying sheet and over said axis; said parallelpullers being affixed to said lower edge of said bulkhead and to saidsecond draw bar; said series of parallel pullers comprising said firstpair of cables.
 3. The truck box as claimed in claim 1 wherein saidsides have a respective rail between said upper corners thereof and saidbulkhead having two saddle members engaged onto said rails.
 4. The truckbox as claimed in claim 3, wherein said second pair of cables formingrespective closed loops around said sides.
 5. The truck box as claimedin claim 4, wherein said second pair of cables being connected to saidupper edge of said bulkhead and to said second draw bar by means ofcrimp-type connectors.